From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 19 May 2000 16:55:02 +0100 From: "Stephen C. Tweedie" Subject: Re: PATCH: Enhance queueing/scsi-midlayer to handle kiobufs. [Re: Request splits] Message-ID: <20000519165502.G9961@redhat.com> References: <00c201bfc0d7$56664db0$4d0310ac@fairfax.datafocus.com> <200005181955.MAA71492@getafix.engr.sgi.com> <20000519160958.C9961@redhat.com> <20000519084842.A3373@skull.piratehaven.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20000519084842.A3373@skull.piratehaven.org>; from bapper@piratehaven.org on Fri, May 19, 2000 at 08:48:42AM -0700 Sender: owner-linux-mm@kvack.org Return-Path: To: "Stephen C. Tweedie" , Chaitanya Tumuluri , Eric Youngdale , Alan Cox , Douglas Gilbert , linux-scsi@vger.rutgers.edu, chait@sgi.com, linux-mm@kvack.org List-ID: Hi, On Fri, May 19, 2000 at 08:48:42AM -0700, Brian Pomerantz wrote: > > The real solution is probably not to increase the atomic I/O size, but > > rather to pipeline I/Os. That is planned for the future, and now there > > That really depends on the device characteristics. This Ciprico > hardware I've been working with really only performs well if the > atomic I/O size is >= 1MB. Once you introduce additional transactions > across the bus, your performance drops significantly. I guess it is a > tradeoff between latency and bandwidth. Unless you mean the low level > device would be handed a vector of kiobufs and it would build a single > SCSI request with that vector, ll_rw_block can already do that, but... > then I suppose it would work well but > the requests would have to make up a contiguous chunk of drive space. ... a single request _must_, by definition, be contiguous. There is simply no way for the kernel to deal with non-contiguous atomic I/Os. I'm not sure what you're talking about here --- how can an atomic I/O be anything else? We can do scatter-gather, but only from scattered memory, not to scattered disk blocks. --Stephen -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux.eu.org/Linux-MM/